This invention is in the field of press brake tooling used to bend sheet metal workpieces, and particularly to the dies and die holders employed in such tooling.
Tooling for use with a press brake commonly includes a horizontally elongated punch having a downwardly-facing, generally V-shaped punch tip, and a horizontally elongated die that has an upwardly open, generally V-shaped workpiece-contacting portion adapted to receive the punch tip in a workpiece bending operation.
Because of the substantial forces involved in bending operations, it is important that the punches and dies be kept in alignment to avoid undue wear or, more importantly, breakage with resulting danger to press brake operators. Commonly, the press brake punch is fixed in position, and the press brake die, mounted in a press brake die holder, can be positionally adjusted into precise alignment with the punch tip. The die holder is then locked in position for the purpose of restraining lateral movement between punch and die.
Press brake dies commonly have a downwardly extending tang, generally rectangular in cross section, that is received in an upwardly open, complimentary shaped slot in a die holder. Set screws, inserted from the side of the die holder, may be employed to lock the tang within the holder slot. More commonly, however, the fit between the die tang and die holder is sufficiently close that no further locking is provided, and as a result, the die can be removed from he die holder with some ease.
Particularly in the latter case, however, in which a generally rectangular tang is received in a complimentary shaped slot in the die holder, some slight back and forth rocking motion or xe2x80x9cwobblexe2x80x9d of the die within the holder occurs, and is difficult to avoid. A very small amount of wobble or play between the die tang and the slot is magnified at the level that the upper surfaces of the die meet the punch tip. It is difficult to economically obtain tolerances between the die tang and die holder that would prevent such movement. If most of the wobble is to be avoided through the use of extremely close tolerances in the machining of the tang and slot, the cost of machining may become economically prohibitive. Also, the use of very close tolerances between the tang and die holder renders it difficult to properly insert the tang into and remove the die from a die holder.
Various die and die holder combinations are shown in U.S. Pat. No. 4,787,237 (Houston et al.) and U.S. Pat. No. 3,702,558 (Swenson et al.). It would be desirable, without requiring the presence of set screws or the like to rigidly position a die in a die holder, to provide a die and die holder in which the die could be easily inserted in and removed from the die holder, but, once inserted, the die would be restrained from wobble with respect to the die holder.
We have found that we can employ one or more resilient plugs that protrude into the slot of the die holder to resiliently urge the tang of the die against one of the walls forming the slot in the die holder, thereby restraining wobble in the die.
In accordance with one aspect of the invention, the invention relates to a press brake die holder for holding a die having an upper, work-contacting surface and a lower, elongated tang in which the die comprises a body having a slot defined by opposing walls and adapted to receive between them the tang of the punch. At least one of the walls is provided with a cavity opening into the slot, and a resilient plug is received and retained in the cavity and protrudes into the slot toward the other wall. As the tang of the die is received in the slot, the resilient plug urges the tang resiliently into contact with the other wall to restrain the tang from wobbling in the slot.
The tang of the die is generally rectangular in shape, having generally parallel, vertical walls. Similarly, the slot of the die holder is rectangular in cross section, having opposed walls that confront the parallel, vertical walls of the tang. Preferably, the plug and the cavity in which the plug is received desirably are elongated in a direction parallel to the plane of the wall from which the plug protrudes.
In one preferred embodiment, a plurality of spaced, generally vertical bores is formed in the die holder body adjacent one of its walls, with the bores opening into the slot. Resilient, generally cylindrical plugs are received in the respective bores and protrude into the slots to contact the confronting wall of a die tang and force that tang against the opposing slot wall to thus restrain the die from wobbling in the die holder.
In another preferred embodiment, the bore or bores formed in the die holder body adjacent one of its walls extend instead in the long direction of the die holder, that is, generally horizontally, and open onto the slot. One or more resilient, generally cylindrical plugs are received in the respective bores and protrude into the slot to contact the confronting wall of a die tang and force that tang against the opposing slot wall to thus restrain the die from wobbling in the die holder.